The mammalian retina contains at least 3 major classes of output cells, X-, Y-, and W-cells. These differ in receptive field properties, morphology, axon conduction velocity, and central destination of their axons. In the cat, the various subdivisions of the thalamic relay complex of the retina, the lateral geniculate nucleus (LGN), differ both in the proportions of X-, Y-, and W-cells projecting to them from the retina, and in the pattern of their projections to the visual cortex. The manner in which the outputs of these subdivisions interact at the vivual cortex is not understood. I propose to investigate the differential roles of the LGN subdivisions in areas 17 and 18 of the cat visual cortex. This will be done by reversibly blocking activity of a discrete portion of a particular subdivision with microinjections of the local anesthetic lidocaine. Before, during, and after recovery from the block, response properties of individual neurons in the region of area 17 or 18 receiving input from the anesthetized area will be quantitatively assessed. By knowing how cortical neurons behave with and without these inputs, I hope to deduce the contributions of the individual subdivisions to cortical function. Results from this investigation may help answer the basic question of how parallel systems are used by the brain in the analysis of the visual image.